Six Britons have been arrested on suspicion of being involved in running online drug marketplace Silk Road 2.0 and one other illegal website.

The arrests were part of a joint European and US operation stretching across 17 countries and culminating in the shutdown of over 400 other illicit web sites and services not usually accessible through normal search engines or by typing out standard web addresses.

UK police revealed that more British nationals involved in the “dark web” global trade of illegal drugs, forged documents and firearms will be arrested as part of the National Crime Agency’s (NCA) “project protein”.

The alleged founder of the site, 29-year-old Ross William Ulbricht, who went by the name Dread Pirate Roberts, is currently standing trial in the United States. Ulbricht denies the charges against him.

The new Silk Road 2.0 site began trading a year ago and is believed to have been resurrected by former administrators of the old site, allowing more than 100,000 people to buy and sell illegal drugs and other contraband, US prosecutors said.

The NCA described the six British arrests as “significant”, adding that a large amount of computer equipment has been seized at all the addresses searched and will now be forensically examined.

The six – a 20-year-old man from Liverpool, a 19-year-old man from New Waltham in Lincolnshire, a 30-year-old man from Cleethorpes, a 29-year-old man from Aberdovey in Wales and a man and woman, both 58, also from Aberdovey, have all been bailed after being interviewed.

The head of Europol’s cyber crime unit, Troels Oerting, told the Guardian that 40 digital investigators collaborated on one of the biggest dark-web takedowns to date. Following the six-month-long investigation police have seized drugs, guns, and €180,000 in cash, gold and silver, and $1m worth of bitcoin virtual currency.

Police added that technical infrastructure key to the hosting of illegal marketplaces on the dark web had also been dismantled.

“We are not ‘just’ removing these services from the open internet,” said Oerting. “This time we have also hit services on the dark net … where, for a long time, criminals have considered themselves beyond reach. We can now show that they are neither invisible nor untouchable.”

Police have also taken down sites going by the name of Cloud Nine, Hydra, BlueSky, Outlaw Market and Alpaca.

In a statement the NCA’s deputy director, Roy McComb, was clear other arrests would be made as part of the operation. “Over the months since the original Silk Road was taken down, we have been working with partners in the US and Europe to locate technical infrastructure key to the dark web and to investigate individuals suspected of significant involvement in illegal online market places.

“Those arrested by the NCA in this phase of the operation are suspected of setting up Silk Road 2.0, or of being significant vendors of illegal drugs. The operation is ongoing and more arrests can be expected as we continue to investigate those involved in setting up and profiting from these illegal marketplaces.”

Warning that criminals wouldn’t stay anonymous by using the dark web, McComb said: “Criminals like to think that the dark web provides a safe, anonymous haven but in reality this is just like any other organised crime network. It may take time and effort to investigate and build a criminal case, but we are determined to identify and prosecute people caught dealing drugs and committing serious crime using the dark web.”

Speaking alongside Bill Bratton, the commissioner of the New York police department, at a counter-terrorism conference in New York, Hogan-Howe claimed the internet was at risk of becoming a “dark and ungoverned space” which was “frustrating the efforts of police and intelligence agencies to keep people safe”.